I really like the idea of a design where the pot and front of the furnace are basically a cart that can lower and roll out for changes. The current design where you have to move the most fragile and critical parts of your furnace (elements, crown) to get to the part you're going to trash (old pot) seems like it could use some re-engineering.

Even in a kiln car design. you had better pull the elements. Things get stuck together in a glass furnace and getting them loose takes force. The difficulty in the design in which the crown remains in place is always the same- the span of the crown that is unsupported.

Lets say you have the castings for a 400# stadelman, and a 200# pot. cutting about 8” or so off the length of the three curved wall castings lowering the overall interior height but allowing the heating elements to hang between the 200# pot and the larger diameter 400# wall castings. this would lower the furnace height allowing more room to pull the heaters and get some heat down lower too….…..and if’n you don’t like the castings maybe just use those tiny tiny ifb to lay up a chamber like they did in the Norway furnace.

Or preferably use some hard bricks instead of the IFB's.
You'd have to know someone with a huge diamond saw to cut the castings down I'd imagine. Sounds interesting as far as getting elements lower and more room for them around outside of pot, but wouldn't you be sacrificing space for your soft insulation between the casting and the steel exterior? Unless you expand the steel shell as well I suppose.

Have folks had problems with breaking the crowns on moly furnaces while doing a pot change? If it sounds like the elements and passage bricks need to be removed even if the furnace design is a front-pot access, is it that much more problematic to remove the crown too and stick with the more straightforward top-pot change design which should allow for maximum structural integrity of the furnace?

In conversation with Charlie this morning, he want to pull the pot from the crown. He says he has an evenly split crown with arch support and that it works great, so I am going along with his design since he has built a boatload of them. The trouble with my rectangle is that there is a lot of unused space you have to pay to heat. This doesn't bother me and I put three pots in the furnace anyways, not one. I do it out the front because I've always done it out the front.

You have to pay attention to the watt loading that each element provides based on both the hot and the cold zones. Each one changes as it's sizing changes. Mine runs about 20,000 watts. The wattage has to be able to drive the size of the furnace or you will have the equivalent of a VW bug on a hill with a ton of lead in the back seat. One of the big troubles with the wire furnaces which are really just converted ceramic kilns is that while they might have the physical capacity for a large pot, they do not have the amps to get it hot enough to not drive a pro shop nuts.

Have folks had problems with breaking the crowns on moly furnaces while doing a pot change? If it sounds like the elements and passage bricks need to be removed even if the furnace design is a front-pot access, is it that much more problematic to remove the crown too and stick with the more straightforward top-pot change design which should allow for maximum structural integrity of the furnace?

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The problem I see with the existing crowns are that they are flat, not arched. Most of the parts replacements we are doing are related to the kind of glass being melted. Sadly the Spectrum nuggets are a common denominator in most of the parts failures. We just finished a long test comparing Engineered Ceramics pot to High Temp pots using the nuggets. In both cases the pots experienced really substantial pitting in short order to the point where we are just not going to recommend high alumina pots to people insisting on using Nuggets anymore. Our next set of tests will involve melting SP87 in the same containers and seeing how they do comparatively. We will have all the test samples at Seattle GAS. What was interesting in the testing was that there were no signs of free alumina in the melted glass which would indicate to me that the China Clays in the formulation are what is being attacked and dissolved readily. You have to have some clay in the mix. . That would be consistent with the damage we see on fireclay and silicate parts to the furnaces as well. ( the door area).

The other thing that has to be considered in these failures is operator inexperience. It's quite formidable in many cases. The bigger furnaces have the biggest problems. Anything above a 24 inch pot has a very big unsupported area and the crown really wants to sit down.

When I last visited Glass Eye about 6 years ago they had an Italian furnace (Fiorni--sp?). It seemd to be designed so that (to change pots) the entire bottom was unbolted and the old crucible dropped out along with its insulation and steel jacket. Remove and discard, then bring in the new component, jack it up to position and replace the fasteners. (It was a gas-fueled unit, if I recall.) Seemed like a good approach.

You can roll the furnace out with the elements in place. You'll be going about six feet or so and the concrete floor should be a smooth ride. I don't know that I've ever had one break from rolling a furnace around, even on less than perfect floors.

I've thought a lot about those designs Lawrence and I haven't ever got past that one problem. Steel will fail. Try and keep things simple. Don't overbuild it.

say I put a piece of half inch in a forge and let it get white hot, unless the steel is upset or stressed it shouldn’t lose shape until somewhere around 2600f. so…how fast would the steel ring fail, wouldn’t it be the equivalent of an annealing every time it cooled to change out the pot and likely last at least as long as the castings?

Btw,..I ordered the Stadelman 200# castings and a pot the other day ...keepin-it-simple

I've tried venting with a 1" inside diameter vent out the top. Using the nuggets, the vent was destroyed quickly. Buildup around the ceramic tube and then eventually total failure, meaning the tube dissolved.
In the larger furnaces, I can't imagine anything working to vent the nugget fumes. It's like trying to find a container for the world's strongest acid.
Now with SP, and no vent, I've really not seen a need for venting, at least for my 250 lb. and 80 lb. furnaces.

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